..::Demystifying the "Magic Bean"::..

		I am sure that many of us are familiar with the "Magic Bean" which hit the shelves of many gift stores of Singapore in 2006. For those who do not know what it is, the "Magic Bean" is actually a large, pink coloured bean that had been etched with short messages such as "I love you". The seed is stuffed inside a decorative tin can and together with some vermiculite, which it is to be grown in, the "Magic Bean" was marketed initially as a gift item for Valentine's Day that shy individuals could use to convey their feelings. By just adding water and a short wait of a couple of days, an over-sized bean seedling wakes from its dormancy and reveals the secret message on its gigantic cotyledons to its recepient.
Above: Magic Bean growing kit.

Above: Chinese New Year greetings and a lucky lottery
number that were etched onto the seed.

The words were reportedly etched onto the seed using a laser beam. Beans encoded with lottery numbers or festive greetings can now be found on sale in the market. The original tin cans have made way for innovative yet attractive containers like those seen during the recent Chinese New Year this year, where beans bearing auspicious slogans are contained inside gold painted plastic or clay eggs.

Above: The large trifoliate leaves of the Sword Bean.

The bean seedling usually sheds its message-encoded seed leaves within a fortnight and is discarded thereafter. Some sentimental individuals feeling for the innocent, weak-looking seedling would transplant it into a large pot or into the ground to grow. The seedling will put out its large trifoliate leaves and the vine that eventually result will twine around any support it can find.

Above: The Sword Bean is a rampant vine.

Given the right conditions, the seedling will turn into a large, vigorous climber in about two months. From the third month onwards, it should produce arching sprays of red or white coloured flowers. These will form into long green and flat bean pods. When allowed to mature and dry on the vine, the pod, when split, will yield the familiar-looking pink beans, and of course, sans the laser-etched words.

The pod and seeds of C. ensiformis (left) and C. gliadata (right).

So what is the actual identity of the 'Magic Bean'? The common name of the "magic bean" is actually the "Sword Bean", due to the seed pod's resemblence to the blade of a sword and its Malay name is in fact "Kacang Parang". Botanically, it is known as Canavalia gliadata and originates from tropical Asia and Africa. The Sword Bean has a close relative, the Jack Bean, Canavalia ensiformis, which originates from South and Central America. Both species are easily confused with one another. Both legumes are grown as a green manure, or cover crop and used as a fodder, which is not very palatable to livestock.

The inflorescence (left) and flowers (right) of Canavalia ensiformis.

The young pods of both beans are actually eaten as a vegetable in tropical Asia and pickled in Japan. The mature seeds are a good source of protein but should never be eaten raw as they contain a toxic amino acid, canavanine, which is an anti-metabolite of arginine. Canavanine has been found to be cytotoxic to human pancreatic cancer cells. Lectins - concanavalin A and B found in the mature seed can inhibit the absorption of nutrients by the gut. Overnight soaking of the seeds and boiling them in excess water will significantly reduce the canavanine content in them. Heating will also denature the antinutritive lectins. The soaking and cooking water should be discarded. The seeds are also a source of urease, which is used in molecular biology. The Chinese Materia Medica documents the use of the dried seeds of the Sword Bean, Semen Canavaliae, as possessing the properties of being able to warm the spleen and stomach, causing qi to descent and supplementing qi in the kidneys.

Close-up of a seed of
C. gladiata (left) and C. ensiformis (right).

Mature plants of both species are difficult to distinguish from one another. Pod sizes of both species have very slight differences in terms of length and width. Perhaps the only feature that can be used to tell the two species apart is the difference in the appearance of the seeds. The seed of the Jack Bean is smaller and ivory white in colour. Its hilum less than half as long as the seed of the Sword Bean. The seed of the Sword Bean is usually red or pink, and is rarely white. The hilium refers to the small scar where the seed was attached to the parent plant, in this case, part of the fruit.

A young pod (left) and half-mature pod (right) of C. ensiformis.

Both Sword and Jack Beans are relatively easy to grow in Singapore, almost impossible to not succeed. The seeds germinate readily within a week. Because the vines are rampant and sprawling, a large trellis needs to be erected for them to climb on. Both legumes are not fussy about soil type and fertility and are relatively drought-resistant. Give the plants plenty of room to grow - plants in row are to be spaced 60 cm apart and 90 cm between two adjacent rows. The vines are best grown under full sun but are tolerant of some shade. Provide a good base of a balanced fertiliser before sowing of seeds and feed with a flowering and fruiting fertiliser only occasionally during growth. Overfeeding with nitrogen may depress the yield of pods. Most importantly, these plants are seldom bothered by pests and diseases.

BIBLIOGRAPHY

Ekanayake, S., Skog, K., Asp N.G. 2006. Canavanine content in sword beans (Canavalia gladiata): Analysis and effect of processing: Food Chem Toxicol. [In Press]

Purseglove, J.W. 1974. Tropical Crops: Dicotyledons. London: Longman.

Swaffer, D.S., Ang, C.Y., Desai, P.B. and Rosenthal, G.A. 1994. Inhibition of the growth of human pancreatic cancer cells by the arginine antimetabolite L-canavanine. Cancer Res. 54:6045-6048.

Swaffer, D.S., Ang, C.Y., Desai, P.B., Rosenthal, G.A., Thomas, D.A., Crooks, P.A. and John, W.J. 1995. Combination therapy with 5-fluorouracil and L-canavanine: In vitro and in vivo studies. Anti-cancer Drugs 6:586-593.

Tindall, H.D. 1983. Vegetables in the Tropics. London: Macmillan Press.

Chu, Y.P. 1998. Chinese Materia Medica: Chemistry, Pharmacology and Applications. Australia; Amsterdam: Harwood Academic.